The present invention relates to searchlights and more particularly to covert infrared filters for selectively filtering the light source of a searchlight.
Vehicles, such as aircraft and more particularly helicopters, generally have searchlights mounted thereon for providing illumination during take-off, landing, or during search operations. Searchlights may also be useful for identifying aircraft or providing primary or supplemental lighting during operation of the aircraft in adverse conditions, including night operations, rain, and other particle storms. Alternatively, searchlights may be hand held or used in a smaller configuration, such as a flashlight, headlamp, or night vision imaging device.
With the increased use of night vision imaging systems for covert operations, a need has arisen for landing lights, searchlights, and portable light sources that are capable of filtering out visible light and illuminating an area solely with infrared light. While separate infrared and visible spectrum lights may accomplish this objective, there has been recognized a need in the art for a light source which may be converted between infrared and visible illumination.
One method of early convertible night-vision compatible lighting systems utilized a filter over the searchlight cover that allows only infrared light to pass through the filter. This type of filter, however, may be undesirable because of the difficulty in removing or altering the filter, requiring manual access to the searchlight. This limitation restricted the usefulness of the product by limiting flights to either visible-light or infrared-light.
A further improvement was the use of a lamp within a lighting system that has both a visible and an infrared filaments, allowing the operator to switch between the two. Further controls allowed the lamp head to be extended, refracted, and rotated through the use of electrical relays and a selector switch. One example of this improvement is described in U.S. Pat. No. 5,695,272 to Snyder et al.
This improvement allowed significant advantages over the prior art, including the ability to switch between the infrared and visible light spectrum from within the cockpit, thereby eliminating the need to manually remove and replace the searchlight cover to switch modes. However, these lamps do not emit the same intensity as a dedicated infrared or visible light system as the bulb surface is divided between infrared and visible light filtering covers.
U.S. Pat. No. 6,962,423 to Hamilton et al. describes another multi-mode visible and infrared lighthead for use as a landing light or searchlight. This patent describes two separate diodes, one for emitting infrared and the other for emitting visible light, spaced apart in a searchlight with each diode having its own reflector and lens cover. However, this arrangement similarly limits the amount of light that may be transmitted from the searchlight by dedicating a portion of the light-producing elements to only the infrared or visible spectrum.
Another dual mode searchlight is described in U.S. Pat. No. 7,518,133 to Giffen et al. This integrated searchlight lighthead includes separate infrared and visible light illumination sources each positioned within a reflector. The reflectors are merged and separated by an insulating material and air gap, providing cooling of the illumination sources. The merged reflector assembly provides an improved light distribution over previous light sources. However, the merged reflectors are inferior to a single reflector and the combination of separate lighting elements reduces the intensity of the light that may be produced.
Therefore, there has been recognized a need in the art for an improved searchlight capable of selectively transmitting infrared or visible light. There is further a need in the art for an improved searchlight which can be easily switched between infrared and visible illumination without the need for modification of the searchlight housing or cover. Finally, there is a need in the art for an improved searchlight which improves light distribution and efficiency.